Independent heating of samples in a sample holder

ABSTRACT

There is described a method for heating a sample material in a sample holder, the method comprising receiving the sample holder in a heating chamber of a heating system, the sample holder having at least one sample recipient with the sample material therein; dynamically forming an individual mini microwave cavity around the sample recipient; and applying microwaves generated by at least one microwave generator directly to the sample.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of patent application Ser. No.14/466,117 filed on Aug. 22, 2014, which is a divisional of patentapplication Ser. No. 13/025,469 filed on Feb. 11, 2011, which claims thebenefit of U.S. Provisional Patent Application No. 61/304,387, filed onFeb. 12, 2010, the contents of which are hereby incorporated byreference.

TECHNICAL FIELD

The present application relates to the field of sample holderarrangements and systems used in digestion and/or extraction forprocesses such as analytical spectroscopy and chromatography.

BACKGROUND OF THE ART

In order to perform digestion of a sample, the sample is usually placedin an open-ended recipient which is then closed and heated in amicrowave oven. Some digestion systems only allow the heating of asingle sample at a time and therefore a single sample holder is used.This practice is particularly time-consuming.

Other digestion systems allow several samples to be concurrently heatedand so a multi-sample holder is used. These types of sample holders areusually generic racks that receive multiple open-ended recipients, suchas test tubes.

For some digestion processes, heating may result in a large excesspressure in the recipient. To prevent damage or explosion, a valve isprovided that automatically opens if a given internal pressure exceeds athreshold. Special sealing caps are used on the open-ended recipient toprovide this function. However, having to manipulate such a sealing capfor each sample recipient is also time-consuming.

Therefore, there is a need for an improved system that is adapted forthe specific needs of a digestion process for multiple samplesconcurrently.

SUMMARY

In accordance with a broad aspect, there is provided a heating systemfor independently heating at least one sample recipient containing asample, the sample recipient provided in a sample holder, comprising: aheating chamber having at least one opening and adapted to receive thesample holder; at least one microwave generator for generatingmicrowaves; at least one microwave applicator inside the heating chamberconnected to the at least one microwave generator, the at least onemicrowave applicator comprising an oven cavity portion for creating amini microwave cavity around a single sample recipient in the sampleholder, and for applying microwaves generated by the at least onemicrowave generator directly to the single sample recipient; and acontrol unit for controlling the at least one microwave generator.

In accordance with a second broad aspect, there is provided a method forheating a sample material in a sample holder, the method comprising:receiving the sample holder in a heating chamber of a heating system,the sample holder having at least one sample recipient with the samplematerial therein; dynamically forming an individual mini microwavecavity around the sample recipient; and applying microwaves generated byat least one microwave generator directly to the sample.

In accordance with a third broad aspect, there is provided a sampleholder for decomposition or extraction of a sample material, the sampleholder comprising: a frame having a top plate and a base, the top platehaving at least one aperture for receiving a sample recipient holdingthe sample material; at least one partial mini cavity provided betweenthe top plate and the base, the at least one partial mini cavity havingreflecting material on a sample facing surface to reflect microwavestowards the sample material in the sample recipient, and shaped to matewith a complementary partial mini cavity in a heating chamber of an ovensuch that when combined, the partial mini cavity and the complementarypartial mini cavity form a complete and substantially hermetic minimicrowave cavity around the sample recipient.

In one embodiment, the term “sample” refers to a mixture of material tobe decomposed and at least one chemical decomposition reagent. Inanother embodiment, the term “sample” refers only to the material to bedecomposed. While the sample recipients may sometimes be referred to as“tubes”, it should be understood that they should not be limited tocircular in shape. In addition, the term “digestion” should beexchangeable with the term “extraction” throughout the description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a sample holder system, in accordancewith an embodiment;

FIG. 2 is a perspective view of a rack of the sample holder system ofFIG. 1, in accordance with an embodiment.

FIG. 3 is a perspective view of a rack cover of the sampled holder ofFIG. 1 with compression caps attached thereto, in accordance with anembodiment;

FIG. 4 is a bottom perspective view of a cap-receiving plate of the rackcover of FIG. 3 with compression caps attached thereto, in accordancewith an embodiment;

FIG. 5 is a bottom perspective view of a clamping bar of the rack coverof FIG. 3, in accordance with an embodiment;

FIG. 6 is a perspective view illustrating the securing of the clampingbar of FIG. 5 to the rack of FIG. 2, in accordance with an embodiment;

FIG. 7 is a perspective view of a rack cover provided with a safetymechanism, in accordance with an embodiment;

FIG. 8a is a partial side view of the rack cover of FIG. 7 secured to arack, in accordance with an embodiment;

FIG. 8b is a blown-up perspective view of the rack cover of FIG. 7,showing the safety mechanism in more detail, in accordance with anembodiment;

FIG. 9a is a partially sectional perspective view of a compression capto be secured in the cap-receiving plate of FIG. 4, in accordance withan embodiment;

FIG. 9b is another embodiment of a partially sectional perspective viewof a compression cap, with a lock washer added;

FIG. 9c is yet another embodiment of a partially sectional perspectiveview of a compression cap, with the order of parts reversed;

FIG. 10a is an exploded perspective view of the compression cap of FIG.9a , in accordance with an embodiment;

FIG. 10b is an exploded perspective view of the compression cap of FIG.9b , in accordance with an embodiment;

FIG. 10c is an exploded perspective view of the compression cap of FIG.9c , in accordance with an embodiment;

FIG. 11a is a perspective view of the rack of FIG. 2 accommodating tubesclosed by sealing caps, in accordance with an embodiment;

FIG. 11b is a perspective view of the rack without any tubes, withmicrowave reflecting cylinders, in accordance with an embodiment;

FIG. 12 is a cross-sectional view of a sealing cap, in accordance withan embodiment;

FIG. 13 is a cross-sectional view of a test tube covered by the sealingcap of FIG. 12, in accordance with an embodiment;

FIG. 14 illustrates forces exerted on a slot member of the clamping barof FIG. 5 when inserted into a rectangular slot of a stud of the rack ofFIG. 2, in accordance with an embodiment;

FIG. 15 illustrates a cross-sectional view of a slot member of theclamping bar of FIG. 5 when inserted into a slot having a matchingshape, in accordance with an embodiment;

FIG. 16 is a graph of coefficient (μ, α) as a function of coefficient offriction μ and angle α, in accordance with one embodiment;

FIG. 17 is a perspective view of a rack comprising a removabletransportation plate and covered by a rack cover, in accordance with anembodiment;

FIG. 18 is a perspective view of a transportation plate, in accordancewith an embodiment;

FIG. 19A is a cross-sectional view of a sample tube provided with aflange, in accordance with an embodiment;

FIG. 19B is a cross-sectional view of a sample tube having a varyingdiameter, in accordance with an embodiment;

FIG. 20 is a perspective view of sample tubes when received on thetransportation plate of FIG. 18, in accordance with an embodiment;

FIG. 21 is a perspective view of the transportation plate and the sampletubes of FIG. 20 when received in a holding frame, in accordance with anembodiment;

FIG. 22 is a perspective bottom view of the rack of FIG. 17, inaccordance with an embodiment;

FIG. 23 is a block diagram of an automated digestion system comprising astraight conveyor extending through a microwave oven, in accordance withan embodiment;

FIG. 24 is a block diagram of an automated digestion system comprising aU-shaped conveyor extending through a microwave oven, in accordance withan embodiment;

FIG. 25 is a block diagram of an automated digestion system extendingthrough a microwave oven and a cooling chamber, in accordance with anembodiment;

FIG. 26 is a cross-sectional side view of a cooling chamber, inaccordance with an embodiment;

FIG. 27 is a block diagram of an automated digestion system comprising astraight conveyor extending through a microwave oven, a cooling chamber,and an auto-venting chamber, in accordance with an embodiment;

FIG. 28 is a cross-sectional side view of an auto-venting chamber, inaccordance with an embodiment;

FIG. 29 is a block diagram of an automated digestion system comprising aconveyor extending through a microwave oven, a cooling chamber, and anauto-venting venting chamber, in accordance with an embodiment;

FIG. 30 is a photograph of an automated digestion apparatus, inaccordance with an embodiment;

FIG. 31 is a block diagram illustrating a first disposition of sampleholders on a conveyor, in accordance with an embodiment;

FIG. 32 is a side view of a conveyor belt, in accordance with anembodiment;

FIG. 33 is a block diagram illustrating a second disposition of sampleholders on the conveyor of FIG. 31, in accordance with an embodiment;

FIG. 34 is a block diagram illustrating a third disposition of sampleholders on the conveyor of FIG. 31, in accordance with an embodiment;

FIG. 35 is a block diagram illustrating a fourth disposition of sampleholders on a conveyor, in accordance with an embodiment;

FIG. 36 is a block diagram illustrating a fifth disposition of sampleholders on the conveyor of FIG. 31, in accordance with an embodiment;

FIG. 37 is a block diagram of a heating chamber provided with microwaveapplicators comprising movable cavity portions in a retracted position,in accordance with an embodiment;

FIG. 38 is a block diagram illustrating a rack provided with cavityportions, in accordance with an embodiment;

FIG. 39 is a block diagram illustrating the rack of FIG. 38 insertedinto the heating chamber of FIG. 37 when the movable cavity portions arein the retracted position, in accordance with an embodiment;

FIG. 40 is a block diagram illustrating the rack of FIG. 38 insertedinto the heating chamber of FIG. 37 when the movable cavity portions arein the extended position, in accordance with an embodiment;

FIG. 41 is a block diagram illustrating a heating chamber provided withtwo cavity elements having cavity recesses, in accordance with anembodiment;

FIG. 42 is a block diagram illustrating a heating chamber having movablemicrowave applicators, in accordance with an embodiment;

FIG. 43 is a block diagram illustrating a rectangular microwave cavity,in accordance with an embodiment;

FIG. 44 is a block diagram illustrating a circular microwave cavityprovided with a protective element, in accordance with an embodiment;

FIG. 45 is a block diagram of an automated digestion system providedwith a mini cavity microwave oven, in accordance with an embodiment;

FIG. 46 is a top view of mini cavities provided with a temperaturesensor, in accordance with an embodiment;

FIG. 47 is a side view of a rack provided with rack cavity portions anda rack cover having pressure-relief valve caps, in accordance with anembodiment;

FIG. 48 is a perspective view of a closing mechanism for forming minimicrowave cavities, in accordance with an embodiment;

FIG. 49 is a perspective view of a rack provided with rack cavityportions, in accordance with an embodiment;

FIG. 50 is a block diagram of a directional coupler for measuring thepower of a signal transmitted by a microwave generator to a microwavecavity, in accordance with an embodiment;

FIG. 51 is a block diagram of the directional coupler of FIG. 50 whenused for measuring the power of a signal reflected by the microwavecavity, in accordance with an embodiment;

FIG. 52 is a perspective view of the directional coupler comprisingdetecting diodes and connected to a coaxial cable, in accordance with anembodiment; and

FIG. 53 is a schematic representation of a directional couplercomprising Schottky zero bias diodes, in accordance with an embodiment.

It will be noted that throughout the appended drawings, like featuresare identified by like reference numerals.

DETAILED DESCRIPTION

FIG. 1 illustrates one embodiment of a sample holder system 10 ready tobe used for decomposition or extraction of a sample material. Sampleholder system 10 comprises a rack 12, sample tubes 13 with sealing caps14, a rack cover 15 and compression caps 16. The material to beextracted or decomposed is placed inside the sample tubes 13 withchemical decomposition agents such as acids, for example. The rack 12 isused to maintain the sample tubes 13 in an upright position. The sealingcaps 14 hermetically close the opening of the tubes 13. The compressioncaps 16 are secured in the rack cover 15. The rack cover 15 with thecompression caps 16 secured therein is placed on top of the rack 12 sothat the compression caps 16 allow an exhaust of gas when the internalpressure in the tubes 13 exceeds a predetermined threshold value.

The assembly of the compression cap 16 and the sealing cap 14 forms apressure-relief valve and the rim of a tube 13 is the seat of thepressure-relief valve, whereby excess gas can be evacuated from the tube13. The compression cap 16 is adapted to allow the opening of thepressure-relief valve when the internal pressure within the tube 13exceeds the predetermined threshold value.

While FIG. 1 refers to a sample holder arrangement 10 having twelvetubes 13, twelve sealing caps 14 and twelve compression caps 16, itshould be understood that the number of these pieces is exemplary only.The sample holder system could be adapted to receive six tubes, twentytubes, or any other suitable number of tubes.

Referring concurrently to FIGS. 1 and 2, in one embodiment, the rack 12has a base 20, a support plate 21 and three studs 22 as illustrated inFIG. 2. The number of studs 22 is exemplary only. The base 20 presentstwelve recesses 23. The support plate 21 is U-shaped and comprisestwelve apertures 24. Each aperture 24 is positioned on top of and inline with a corresponding recess 23 and the combination of a recess 23with a corresponding aperture 24 allows a tube 13 to be maintained inthe upright position. The recesses 23 and the apertures 24 are sized asa function of the dimensions of the tubes 13, as the tubes will bereceived therein. The studs 22 each have a slot 25. The studs 22 andtheir corresponding slots 25 allow the rack cover 15 to be releasablysecured on top of the rack 12. The support plate 21 is also providedwith a handle 26 on each side. The handles 26 allow an easytransportation of the rack 12. In one embodiment, the central stud isD-shaped at the top to ensure that the rack cover 15 and a transportplate 126 (FIG. 18) are correctly oriented.

The studs 22 may be replaced by any system which allows the rack cover15 to be releasably secured to the rack 12. For example, the studs 22may be replaced by a plate provided with notches to secure the rackcover 15.

FIG. 3 illustrates one embodiment of the rack cover 15 in which thecompression caps 16 are secured. The rack cover 15 comprises acap-receiving plate 50 and a clamping bar 51 which are interconnected toone another through supporting brackets 52. The clamping bar 51comprises three slot members 53 which are designed to slide into theslots 25 of the studs 22 (FIG. 2) in order to removably secure the rackcover 15 to the rack 12. The slot members 53 are located according tothe location of the slots 25 of the studs 22. The clamping bar 51 slidesrelatively to the securing brackets 52 and the cap-receiving plate 50,according to direction A. This translation movement allows the slotmembers 53 to be inserted into the slots 25. When the clamping bar 51 isin a closed position (i.e., when the rack cover 15 is attached to therack 12), the slot members 53 are locked to the studs 22. When theclamping bar 51 is in an opened position (i.e., when the rack cover 15lies on the rack 12 but the slot members 53 are not interlocked into theslots 25), the slot members 53 are not in line with the studs 22,whereby the rack cover 15 may be separated from the rack 12 by beinglifted away.

FIG. 4 illustrates one embodiment of the cap-receiving plate 50 in whichthe compression caps 16 are threadingly engaged. The cap-receiving plate50 is provided with two types of apertures, namely stud-receivingapertures 54 and cap-receiving apertures 55. The stud-receivingapertures 54 are provided in a number equal to that of the studs 22 andthey are located according to the location of studs 22 in rack 12. Thedimensions of the stud-receiving apertures 54 are chosen according tothe dimensions of the studs 22. When the rack cover 15 is installed ontop of the rack 12, the studs 22 are inserted into the stud-receivingapertures 54, in a direction corresponding to B. The studs are removablefrom the stud-receiving apertures in order to change the studs of givenheight for studs of a different height, thereby accommodating tubes of adifferent height.

The cap-receiving apertures 55 are designed to receive the compressioncaps 16. They have a thread (not visible in FIG. 4) so that thecompression caps 16 are screwed therein. The cap-receiving plate 50 alsohas fixing holes 56 which are used to fixedly secure the supportingbrackets 52 by way of bolts, for example. Alternatively, the supportingbrackets can be attached to the cap-receiving plate 50 using anadhesive, or any other removable or permanent mechanical connector. Inone embodiment, the compression caps 16 are permanently secured to thecap-receiving plate 50 while in another embodiment, they are releasablysecured.

FIG. 5 presents a bottom view of one embodiment of the clamping bar 51on which the supporting brackets 52 are attached. The supportingbrackets 52 can be translated along the clamping bar 51 as illustratedby arrow C. This relative movement between the supporting brackets 52and the clamping bar 51 (illustrated by direction A in FIG. 3) allowsthe slot members 53 to be slid into the slots 25 of the studs 22. In oneembodiment, the slot members 53 may have an L shape and be designed witha wedged surface 57 for improving the securing of rack cover 15 to rack12.

FIG. 6 illustrates how the rack cover 15 is secured on the rack 12. Forsimplification purposes, only the base 20 and the studs 22 arerepresented for the rack 12 and only the clamping bar 51 is representedfor the rack cover 15 in FIG. 6. The slot members 53 slide into theslots 25 of the studs 22 according to direction D as a result of atranslation of the clamping bar 51, thereby allowing the rack cover 15to be locked to the rack 12.

FIG. 7 illustrates one embodiment of a rack cover 70 securable on top ofthe rack 12 and comprising a clamping bar 72 provided with a safetymechanism 74 for preventing the clamping bar 72 from unlocking from thestuds 22 of the rack 12. Similarly to the rack cover 15 illustrated inFIG. 3, the rack cover 70 comprises a cap-receiving plate 76 havingcap-receiving apertures in which compression caps 16 are screwed. Theclamping bar 72 is translationally secured to the cap-receiving plate 76in order to slide slot members 78 into respective slots of the rackstuds 22, as illustrated in FIG. 8a . The clamping bar 72 comprises arecess 80 in which the safety mechanism 74 is secured. The safetymechanism 74 comprises a locking member 84 provided with an aperture 86in which a spring 82 b is inserted and an abutment member 88 for matingwith the locking member 84. The abutment member 88 also has a spring 82a and a pin 83. Pin 83 (see FIG. 8b ) moves up and down and iscompletely engaged when the clamping bar 72 is locked. Pins 71 a and 71b act as visual indicators of a locking and unlocking of the clampingbar 72. In this embodiment, one of the pins 71 a, 71 b is green whilethe other one is red. Only the red one is visible when the clamping bar72 is locked. Only the green one is visible when the clamping bar 72 isunlocked. Other ways of providing visual indication of a locked orunlocked state will be readily apparent to those skilled in the art.

The safety mechanism 74 is movable between a closed position and anopened position. The abutment member 88 mates with the locking member 84and is made of flexible material such as plastic for example, in orderto bias the safety mechanism 74 in the closing position. The abutmentmember 88 abuts against the bottom surface of the clamping bar 72 and ispositioned in compression to exert a downward force on the rear end ofthe locking member 84 via the spring 82 a. As a result of the downwardforce, the rear end of the abutment member 88 engages the stud 22 whenthe safety mechanism 74 is in the closed position, thereby preventingthe slot members 78 from dislodging from the stud slots. By exerting alateral force on the front end of the locking member 84, the safetymechanism 84 is brought into the opening position which allows theclamping bar 72 to rearly slide in order to dislodge the slot members 78from the stud slots. As a result of a lateral force exerted on the frontend of the locking member 84, pin 83 is released and moves upwardly,thereby disengaging the abutment member 88 from the stud 22.

While the present description refers to an abutment member 88 forbiasing the safety mechanism 74 in the closing position, it should beunderstood that any adequate mechanical compression device may be used.For example, a coil spring may be inserted in compression between therear end of the locking member and the bottom of the clamping bar 72 todirectly exert a downward force on the rear end.

FIG. 9a illustrates one embodiment of the compression cap 16. Thecompression cap 16 comprises a cap casing 60 which is a hollow cylinderhaving a screw thread 61 on its external surface in order to be screwedinto the cap-receiving apertures 55 of the cap-receiving plate 50. Thecompression cap 16 comprises a chamber accommodating a helical spring62, a pressure-adjusting bolt 63 and a piston 64, and an apertureadapted to receive a pressure arm 65. The chamber and the aperture areconnected so that the pressure arm 65 travels through the aperture andpart of the chamber.

The pressure arm 65 is secured to the piston 64 so as to be biased bythe spring 62 to exert pressure on the sealing caps 14. For example, thepressure arm 65 may present a screw thread on part of its externalsurface and can be screwed into the piston 64, which has a threadedcavity for receiving the pressure arm 65. Alternatively, the pressurearm 65 and piston 64 can be integrated into a single piston piece. Thespring 62 is placed into the cap casing 60 in compression so that abiased force is applied by the spring 62 on the piston 64.

The spring 62 may be of any shape and dimensions. While the compressioncap 16 comprises a spring 62 to apply a biased force on the piston 64and to prevent an exhaust of gas from the tube 13 before the internalpressure in the tube 13 has reached a threshold value, it should beunderstood that the spring 62 can be replaced by any piece that appliesa biased force on the piston 64.

In one embodiment, the spring 62 is made from metal and covered by anacid-resistant plastic sleeve to protect the spring 62 from acid vapoursand avoid corrosion.

In one embodiment, the pressure-adjusting bolt 63 has a fixed positionand no adjustment of the biasing force of the spring 62 is possible. Inthis case, the pressure adjusting bolt 63 may be integral with thecasing 60 of the compression cap 16.

FIG. 9b is another embodiment of the compression cap 16. In thisembodiment, a lock washer 68 has been added. This will be explained inmore detail with reference to FIG. 10b . FIG. 9c is yet anotherembodiment of the compression cap 16, where the order of the variousparts has been reversed. This will be explained in more detail withreference to FIG. 10 c.

FIG. 10a illustrates an embodiment of the cap casing 60 without thepressure arm 65. The cap casing 60 has thread 66 on part of its internalsurface in the chamber. The pressure-adjusting bolt 63 has a screwthread 67 on its external surface. The screw thread 67 corresponds tothe thread 66 so that the pressure-adjusting bolt 63 can be screwed intothe cap casing 60. FIG. 10b illustrates another the embodiment shown inFIG. 9b , whereby an additional lock washer 68 is present. The lockwasher 68 is installed after the spring 62 and is screwed into thebarrel of the cap casing 60 until the spring 68 reaches its appropriatetension. This level of tension is the maximum pressure on thecompression cap 16 of the vessel that the safety mechanism must resistin order that the cap 16 does not release pressure from the vessel. FIG.10c illustrates the embodiment shown in FIG. 9c . The cap casing 60′ isa combination of cap casing 60 and pressure adjusting bolt 63. Thespring 62, piston 64, lock washer 68, and pressure arm 65 are all thesame as in the embodiment illustrated in FIG. 10b , but in a differentorder. This allows calibration to be done from the bottom of the cap(i.e. pressure arm 65) and adjustment of the cap casing 60′ from the topdoes not affect this calibration.

It should be noted that the shape and dimensions of the compression caps16 may vary. For example, the compression caps 16 may have a squareshape and the apertures 24 may be adapted to receive the compressioncaps 16. The compression caps 16 may also be secured to the rack cover15 by way of screws or clamps for example.

When it is screwed into the cap casing 60, the pressure-adjusting bolt63/lock washer 68 compresses the spring 62. It results in an increasedbiased force exerted by the spring 62 on the piston 64. When theinternal pressure increases in the tube 13, an upward vertical force isapplied on the piston 64 through the sealing cap 14 and the pressure arm65. The piston 64 cannot move as long as the biased force applied by thespring 62 is superior or equal to the upward vertical force resultingfrom the pressure increase in the tube 13. The internal pressure in thetube 13 which creates an upward force applied on the piston 64 that isequal to the biased force applied by the spring 62 on the piston 64corresponds to a threshold pressure. This threshold pressure can becontrolled by adjusting the position of the pressure-adjusting bolt63/lock washer 68 within the cap casing 60.

When the internal pressure in the tube 13 is inferior to the thresholdpressure, the pressure-relief valve system constituted of thecompression cap 16, the sealing cap 14 and the rim of a tube 13 is in aclosed position and the tube 13 is hermetically closed. When theinternal pressure in the tube 13 exceeds the threshold pressure, thepressure-relief valve system is in an open position and gas can exhaustfrom the tube 13. This relief of gas limits the internal pressure in thetube 13 and prevents damage to or explosion of the tube 13. When theinternal pressure goes back below the threshold pressure, thepressure-relief valve system hermetically closes back the tube 13 sincethe biased force applied by the spring 62 is superior to the upwardforce created by the internal pressure of the tube 13.

In one embodiment, the compression cap 16 and the sealing cap 14 form asame and single piece. In this case, a disk 69 of the pressure arm 65has a shape and a size adapted to act as a sealing cap in order to closethe tube 13. Having a sealing cap and a compression cap as two differentpieces enables the compression cap 16 to be used with different sealingcaps 14 independently of the shape and dimensions of the sealing cap 14.

FIG. 11a illustrates one embodiment of the installation of the tubes 13in the rack 12. The material to be extracted or decomposed is placedinside the tubes 13 with appropriate chemical decomposition agents. Thetubes 13 are positioned through the apertures 24 and rest on therecesses 23. The sealing caps 14 are positioned on top of the tubes 13.The compression caps 16 are threadingly locked into the apertures 55 ofthe rack cover 15 as illustrated in FIG. 4. The compression caps 16 arechosen in accordance with a desired threshold pressure. If an adjustmentof the threshold pressure is required, the location of thepressure-adjusting bolts 63/lock washer 68 within the cap casings 60 canbe adjusted. FIG. 11b illustrates a different embodiment for the rack,with microwave reflecting cylinders (explained in more detail below).

The rack cover 15 with the compression caps 16 thereon is positioned ontop of the tubes 13 in the rack 12. During the positioning of the rackcover 15 on top of the tubes 13, the studs 22 are threaded into theapertures 54 of the rack cover 15 and the cap-receiving plate 50 slidesdown along the studs 22 in the direction of arrow B (FIG. 4). The rackcover 15 with the compression caps 16 secured therein is locked to therack 12 by inserting the slot members 53 of the clamping bar 51 into theslots 25 of the studs 22. The insertion of the slot members 53 isachieved thanks to a translation movement of the clamping bar 51 in thedirection of arrow D (FIG. 6). As indicated above, the middle stud mayhave a D-shaped slot to provide better orientation between the rackcover and the transport plate.

The insertion of the slot members 53 into the slots 25 exerts a downwardforce on the rack cover 15 and on the compression caps 16 as they aresecured to the rack cover 15. This downward force is transferred to thesprings 62 of the compression caps 16 via the bolts 63 or lock washer68. The downward force does not add any extra force adds a furthercompression to the springs 62, which increases the biasing force exertedby the springs 62 on the pistons 64. The downward force resulting fromthe locking of the rack cover 15 allows the tubes 13 to be hermeticallyclosed. As a result, the threshold pressure at which the relief of gasoccurs is the pressure corresponding to an upward force equal to thebiasing force exerted by the springs 62 on the pistons 64 in addition tothe (no extra force) downward force resulting from the insertion of theslot members 53 into the slots 25.

Having the compression caps 16 already installed on the rack cover 15before securing it to the rack 12 allows a gain in time, as eachcompression cap 16 does not have to be screwed and adjustedindependently. It also allows automation of the assembly of the sampleholder system 10. When the sample holder system 10 is assembled, thecap-receiving plate 50 is at a predetermined distance from the base 20.This predetermined distance enables the compression caps 16 to lie onthe sealing caps 14 so that the tubes 13 are hermetically closed whenthe slot members 53 are inserted into the slots 25. If a smalladjustment is required, this can be achieved by turning the bolt 63.Once the assembly is finished, the sample holder system 10 is ready tobe placed into heating equipment, such as a microwave oven, when heat isrequired for decomposition of the material.

In order to dismantle the sample holder system 10, the slot members 53are dislodged from the slots 25 by translating the clamping bar 51 inthe opposite direction of arrow D (FIG. 6). The rack cover 15 is removedfrom the rack 12 by upwardly translating the rack cover 15 along thestuds 25 of the rack 12. The tubes 13 can then be removed from the rack12.

In one embodiment, the sample holder system 10 is placed into aconventional or microwave oven for decomposition of the sample material.After being taken out from the oven, the samples are cooled using airblowers for example. After a predetermined cooling time, the rack cover15 is unlocked by translating the clamping bar 51 in the oppositedirection of arrow D (FIG. 6), thereby dislodging the slot members 53from the slots 25. This allows for an auto-venting of all of the tubes13.

In one embodiment, the rack 12 is provided with at least one temperaturesensor positioned below the recesses 23 in order to measure thetemperature of the tubes 13. In this case, the rack cover 15 is unlockedwhen the temperature of the sample material contained within the tubes13 is below a threshold value. In one embodiment, the rack 12 isprovided with a single temperature sensor for measuring the temperatureof a single tube 13, namely a reference tube, and the rack cover 15 isunlocked when the temperature of the sample material within thereference tube is below the temperature threshold.

The different pieces of the sample holder system 10 may be made ofheat-resistant materials if a conventional oven is used. If the heatingequipment is a microwave oven, the different pieces of the system 10 maybe chosen to be compatible with microwave heating. In one embodiment,the different pieces of the sample holder 10 are made from anacid-and-microwave resistant material such as plastic for example.

In one embodiment, at least the studs 22 are removable from the rack 12so that studs of different height may be removably secured to the base20. The height of the studs 22 may be chosen as a function of that ofthe tubes 13. For example, studs having a first adequate height may beused with 50 ml sample tubes and studs having a longer adequate heightmay be used with 75 ml sample tubes. By simply choosing studs having anadequate height, the sample holder 10 can accommodate sample tubes ofdifferent heights.

In one embodiment, the rack cover 15 is first secured to the rack 12 andsubsequently, the compression caps 16 are individually screwed into thecap-receiving plate 50.

While the description refers to sample tubes 13 to receive the materialto be decomposed, it should be understood that any container having anyshape and dimensions can be used as a receiving part. In this case, therack 12 and the sealing caps 14 are adapted to receive the container andto hermetically close the container, respectively.

The sample holder system may be of any shape and size. In particular,any frame adapted to receive the sample tubes 13 can be used and anycover into which the compression caps 16 can be inserted may also beused. While the rack 12 is a hollowed piece, it could be replaced by ablock having holes adapted to receive the tubes 13, for example.

FIGS. 12 and 13 illustrates one embodiment of a sealing cap 100 forsealing a cylindrical sample tube 102. The sealing cap 100 has a tubeengaging side 104 provided with a circular groove 106 and a centralconical protrusion 108. The groove 106 and the protrusion 108 are sizedand shaped so that the rim 110 of the sample tube 102 does not abutagainst the bed surface 112 of the groove 106 when the sealing cap 100is positioned on top of the tube 102, as illustrated in FIG. 13.Therefore, the tube is not hermetically close when the sealing cap 100is positioned on top of the tube 102.

The sealing cap 100 is made from a flexible material so that the groove106 and the conical protrusion 108 may be deformed when the sealing cap100 is positioned on top of the tube 102 and a downward force is exertedon top of the sealing cap 100. The downward force may be exerted by acompression cap such as compression cap 16 for example. As a result ofthe downward force, the walls of the groove 106 hermetically engage therim of the tube 102 to hermetically close the tube 102.

FIG. 14 illustrates an example of forces in action when a slot member 53is positioned in a slot 25 of a stud 22. It should be noted that thisexample is illustrative only and that other scenarios involving same ordifferent forces are also possible. Force T is the force used to pushback the slot member 53 out of the slot 25. Force R is the reactionforce exerted by the stud 22 on the slot member 53. Forces F1 and F2 arefriction forces resulting from the friction of the slot member 53 on thestud 22 when the slot member 53 is pushed back. Force P is the forceresulting from the increase of internal pressure in the tubes 13.

Friction force F1 can be expressed as a function of the force P and acoefficient of friction μ as shown in the following equation:F1=μ*P  (Eq. 1)

The friction force F2 can be expressed as a function of the force R andthe coefficient of friction μ as shown in the following equation:F2=μ*R  (Eq. 2)

Force T is the force resulting from the friction forces F1 and F2 in they-direction and is given by equation 3:T=μ*P+R*(μ*cos α−sin α)  (Eq. 3)

where α is the angle of the wedge of wedged surface 56 of the slotmember 53.

The force R can be expressed as a function of the force P, thecoefficient of friction μ and the angle α according to equation 4:R=P/(cos α+μ*sin α)  (Eq. 4)

Substituting the force R by equation 4 in equation 3, the force T can beexpressed as:T=P*μ+P*(μ*cos α−sin α)/(cos α+μ*sin α)  (Eq. 5)

Equation 6 is a simplified expression of equation 5:T=P*coef(μ,α)  (Eq. 6)wherecoef(μ,α)=μ+(μ*cos α−sin α)/(cos α+μ*sin α)  (Eq. 7)

Equation 6 shows that the force T is proportional to the force P. As aresult, the force T, which is the force used to push back the slotmember 53 out of the slot 25, is proportional to the increase ofinternal pressure in the tube 13 and is also a function of the angle α.Therefore, it is possible to adjust the force T by controlling the angleα.

While FIG. 14 illustrates a stud 22 having a rectangular slot, it shouldbe understood that the slot may have any adequate shape. For example,FIG. 15 illustrates a stud 22′ provided with a slot having a shapematching that of the slot member 53.

FIG. 16 is a graph of coef (μ, α) as a function of the coefficient offriction μ and the angle α. Two observations can be made from FIG. 8:coef (μ, α) is proportional to the coefficient of friction μ andinversely proportional to the angle α. As a result, the force T is alsoproportional to the coefficient of friction μ and inversely proportionalto the angle α. Decreasing the angle α implies a greater force T to pushback the slot member 53 out of the slot 25. The lower the angle α is,the higher the increase of the internal pressure into the tube 13 has tobe in order to push the slot member 53 out of the slot 25. As a result,it is possible to set the angle α to a value preventing the rack cover15 from being removed from the studs 22 of the rack 12.

In one embodiment, the spring 62 is enclosed in cap casing 60 in acompression state which sets a threshold pressure. For example, spring62 has a length of 1 inch when no forces are applied to it. This springpresents a maximum load of 213.14 lb for a deflection of 37% of itslength. Spring 62 is enclosed within cap casing 60 with a lengthdeflection of 25%. This means that spring 62 presents a load of 144 lb.The internal pressure in tube 13 which can generate the same load isgiven by equation 8:P[psi]=Load[lb]/Surf[in²]  (Eq. 8)

where Surf is the internal surface of tube 13.

For example, if the internal surface of tube 13 is equal to 0.76 in²,the internal pressure corresponding to a load of 144 lb is 189.26 psi.This internal pressure is the threshold pressure corresponding to adeflection of spring 62 equal to 25%. If the internal pressure in tube13 is below 189.26 psi, tube 13 is hermetically closed, and if theinternal pressure is superior to 189.26 psi, the internal pressure issufficient to compress spring 62 and gas can escape from tube 13.

The following example illustrates how the internal pressure thresholdcan be adjusted via the pressure-adjusting bolt 63 or the lock washer68. Table 1 presents the load of the spring 62 and the correspondingthreshold pressure as a function of the displacement Dx of thepressure-adjusting bolt 63/lock washer 68 within the cap casing 60. WhenDx is equal to zero, the pressure-adjusting bolt 63/lock washer 68applies no force on the spring 62, which presents no additionaldeflection. In this case, the load of the spring 62 is 144 lbs, whichcorresponds to a threshold pressure of 189.47 psi. By screwing thepressure-adjusting bolt 63/lock washer 68, an additional compression isapplied to the spring 62, which increases its load. For example, bydisplacing the pressure-adjusting bolt 63/lock washer 68 by 0.2 in, thetotal load of the spring 62 is increased up to 259.2 lb, whichcorresponds to a threshold pressure of 314.05 psi.

TABLE 1 Dx Load Pressure [in] [lb] [psi] 0.000 144.000 189.26 0.025158.400 208.42 0.050 172.800 227.37 0.075 187.200 246.32 0.100 201.600265.26 0.125 216.000 284.21 0.150 230.400 303.16 0.175 244.800 322.110.200 259.200 341.05

For a fixed initial compression of the spring 62, it is possible to varythe threshold pressure at which the pressure-relief valve opens and gasexhausts from the tube 13 from 189.26 to 314.05 psi by screwing thepressure-adjusting bolt 63/lock washer 68.

While the present description refers to slot members 53 to be positionedin slots 25 in order to removably and fixedly secure the rack cover 15to the rack 12, it should be understood that any adequate fastener thatallows removably securing the rack cover 15 to the rack 12 can be used.For example, bolts or screws may be used for securing the rack cover 15to the rack 12.

FIG. 17 illustrates a sample holder system 120 comprising a rack 122, arack cover 124, and a transportation plate 126. The rack 122 comprises abase plate 128 to which a U-shaped support plate 130 is secured. Thesupport plate 130 is provided with twelve apertures each adapted toreceive a sample tube 132, and a pair of handles 134. The rack cover 124comprises a cap-receiving plate 136 to which a clamping bar 138 istranslationally secured. The cap-receiving plate 136 is provided withtwelve apertures each for receiving a compression cap 140.

FIG. 18 illustrates one embodiment of a U-Shaped transporting plate 126comprising twelve tube-receiving openings 142 and three stud-receivingopenings 144. The tube receiving openings 142 are each positioned to bealigned with a respective tube-receiving aperture of the support plate130 of the rack 122, and shaped and sized to receive a tube 132. Thestud-receiving openings 144 are positioned, shaped, and sized to eachreceive a corresponding stud of the rack 122. The transporting plate 126is further provided with a pair of apertures 146 each forming a handle.

It should be understood that the shape, dimensions, position, and numberof the tube-receiving openings 142 and the stud-receiving openings aredetermined in accordance with the shape, dimensions, position, andnumber of the tube-receiving apertures of the support plate 130 and thestuds of the rack 122, respectively.

FIGS. 19A and 19B each provide an example of a sample tube 132 which maybe used with the transporting plate 126 and the rack 122. The sampletube 150 illustrated in FIG. 19A comprises a cylindrical tube 152 havingan opened end 154, and a flange circumferentially extending around thetube 152 adjacent the open end 154. It should be understood that theposition of the flange 156 along the height of the tube 152 is exemplaryonly. For example, the flange 156 could be positioned at about half ofthe height of the tube 152.

The sample tube 158 illustrated in FIG. 19B is a cylindrical tube havinga diameter varying along its height. The tube 158 comprises a firstsection 160 having a constant circumference therealong and awide-mouthed section 162 having an increasing circumference near theopening 164 of the tube 158.

The circumference of the tube-receiving openings 142 is larger than thatof the tube 150 or that of the section 160 of the tube 158 so that thetube 150 or 158 can be inserted into the opening 142. The circumferenceof the tube-receiving openings 142 is smaller than that of the flange156 of the tube 150 or that of the rim of the tube 158 so that theflange 156 of the tube 150 or the wide-mouthed section 162 of the tube158 may engage the surrounding or the rim of the aperture 142 of thetransporting plate 126. As a result, the tube 150 or 158 may besupported by the transporting plate 126.

It should be understood that the shape of the sample tubes 150 and 158is exemplary only. A sample tube to be used with the transportationplate 126 may have any adequate shape as along as at least a portion ofthe tube passes through the tube-receiving aperture 142 while beingsupported by the transporting plate 126. For example, an adequate tubecan comprise two cylindrical section having different diameters.

FIG. 20 illustrates the transporting plate 126 supporting twelve sampletubes 132. Each sample tube 132 is provided with a flange 170 near theopening of the tube 132. The circumference of the tube 132 is inferiorto that of the opening 142 so that it can slide therein, but thecircumference of the flange 170 is superior to that of the opening 142so that the flange 170 is supported by the surrounding of the opening142.

In one embodiment, a protective ring 172 is inserted in eachtube-receiving opening 142 for protecting the rack 126 against the hightemperature of the tube 132. The protective ring 172 can be made fromTeflon for example.

In one embodiment, the transporting plate 126 allows the grouping of aplurality of sample tubes 132 on a same structure. The transportingplate 126 facilitates the transportation of the sample tubes 132 since auser does not have to individually transport the sample tubes 132.

FIG. 21 illustrates a holding frame 180 for holding the transportingplate 126. The holding frame 180 comprises a top plate 182 and a pair ofside plates 184, thereby providing the holding frame 180 with a U-shape.The top plate 182 comprises twelve apertures 186 each sized to receive asample tube 132 and positioned to be aligned with a tube-receivingopening 142 of the transporting plate 126. The side plates 184 eachcomprise an opening 188 forming a handle. The transporting plate 126comprising the sample tubes, as illustrated in FIG. 20, is deposited ontop of the top plate 182 of the holding frame 180 so that each sampletube 132 is received in a corresponding aperture 186. Alternatively, thetransporting plate 126 may be deposited on the top plate 182 and theopenings 142 of the transporting plate 126 are each aligned with arespective aperture 186 of the holding frame 180. Then the sample tubes132 are each inserted into a corresponding tube receiving opening 142,which results in the assembly illustrated in FIG. 21.

The assembly illustrated in FIG. 21 may be used in a preparation stationin which a user fills the tubes 132 with a sample. Once the preparationof the samples is completed, the user may concurrently transport all ofthe tubes 132 by taking the handles of the transporting plate 126 andlifting the transporting plate 126. The user may then insert the tubes132 into the rack 122. First the tubes are each aligned with arespective tube-receiving opening of the rack 122, and then thetransporting plate 126 is pulled down to insert the sample tubes 132into their respective tube-receiving opening until the transportingplate 126 engages the support plate 130 of the rack 122. Once thetransporting plate 126 with the tubes 132 is deposited on the rack 122,the rack cover 124 is deposited on top of the rack 122 to obtain thesample holder system 120 illustrated in FIG. 17. The sample holdersystem 120 is placed into a microwave oven where the samples are heated.Once the digestion is completed, all of the tubes 132 may beconcurrently brought to an analysis station where the user may analysethe digested or extracted samples.

While in FIG. 22 the handles of the support plate 126 are upwardlydirected and engage the support plate 130 of the rack 122, it should beunderstood that the tubes 132 may be inserted in the transporting plate126 so that the handles of the supporting plate 126 are downwardlydirected.

It should be understood that the shape of the holding frame 180 isexemplary only as along as it allows the transporting plate 126 to besupported. For example, the holding frame may comprise a top platehaving tube-receiving apertures and four legs to have a table-likeshape.

In one embodiment, the tube-receiving openings 142 of the transportingplate 126 and/or the tube-receiving apertures of the support plate 130may be identified by an identifier such as a number for example. Forexample, a number comprised between one and twelve may be printed orengraved adjacent to the corresponding tube-receiving opening 142 of thetransporting plate 126 and/or the tube-receiving aperture of the supportplate 130. In another embodiment, only one tube-receiving opening 142 ofthe transporting plate 126 and/or the first tube-receiving aperture ofthe support plate 130 is identified as being the first opening.

It should be understood that the shape of the transportation plate 126is exemplary only as long as it allows at least one sample tube to besupported by a sample structure. For example, the transportation platemay be a rectangular and planar plate provided with twelve apertures, orit may be provided with a single aperture. In one embodiment, twelveindividual transportation plates each holding a single tube are insertedinto the receiving apertures of the holding frame 180.

It should be understood that the rack cover 15 or 70 may be used in thesample holder system 120. Similarly, the rack 122 may correspond to therack 12 provided with studs 22 having an adequate height.

FIG. 23 illustrates one embodiment of an automated microwave oven 200for heating a sample to be extracted or decomposed. The oven 200comprises a heating chamber 202, a microwave generator 204, a conveyor206, and a control unit 208. The heating chamber 202 is adapted toreceive a sample holder 210 containing the sample to be heated. Themicrowave generator 204 is adapted to generate microwaves andoperatively connected to the heating chamber 202 in order to propagatethe generated microwave energy into the heating chamber 202. Forexample, the microwave generator 204 may be positioned in the heatingchamber 202. In another embodiment, the microwave generator 204 isseparate from the heating chamber 202 and a microwave waveguide connectsthe microwave generator 204 to the heating chamber 202 in order totransport and propagate the generated microwaves into the heatingchamber 102.

The conveyor 206 is adapted to receive and transport the sample holder210 through the heating chamber 202 which is provided with an entranceopening 212 and an exit opening 214. An entrance door 216 and an exitdoor 218 are provided for closing the entrance opening 212 and the exitopening 214, respectively. The entrance and exit door 216 and 218 aremade from a microwave-resistant material in order to prevent themicrowaves from propagating outside the heating chamber 202. Theconveyor 206 extends through the heating chamber 202 via the entranceand exit openings 212 and 214. It should be understood that thegeneration of microwaves is stopped when the sample holder 210 enters orexits the heating chamber 202.

The control unit 208 is configured for controlling the conveyor 206, themicrowave generator 204, and the entrance and exit doors 216 and 218.The control unit 208 may be adapted to adjust the power or the dutycycle of the microwaves generated by the microwave generator 204 and/orthe duration of the microwave generation in order to heat the samplecontained in the sample holder 210. The control unit 208 is furtheradapted to control the displacement of the conveyor 206 in order tocontrol the speed of displacement and position of the sample holder 210.The control unit 208 is also adapted to coordinate the opening andclosing of the doors 216 and 218 with the entry and exit of the sampleholder 210 from the heating chamber 210.

In one embodiment, the microwave generator 204 is adapted to control thepower of the generated microwaves. In this case, the control unit mayadjust the power of the generated microwaves to a desired valuecomprised between 0% and 100% of the maximum power of the microwavegenerator 204. The microwave generator 20 is then operated continuouslyduring a predetermined period of time at a desired power to heat thesample at a desired temperature.

In another embodiment, the power of the microwave generator 204 is notcontrollable which means that only the maximum microwave power may bedelivered by the microwave generator 204. In this case, the microwavegenerator 204 operates according to a duty cycle.

In one embodiment, the doors 216 and 218 are each provided with amicrowave quarter-wave trap for preventing any leakage of microwavesoutside of the heating chamber. The oven may also be provided withmicrowave sensor for detecting any leakage of microwaves outside of theheating chamber 202. In this case, the control unit 208 may be adaptedto stop the microwave generator 204 upon detection of a microwaveleakage.

In one embodiment, the control unit 208 comprises a processor, a memory,and a command input device. A user enters parameters such anidentification of the sample, a desired temperature, a desired microwavepower, a heating time, and/or the like, into the control unit 208 viathe command input device.

In one embodiment in which the user enters a desired temperature for thesample, the microprocessor is adapted to determine the microwave poweror the duty cycle corresponding to the desired temperature for thesample. For example, the memory may be provided with a database oftemperatures and corresponding microwave powers, or a database ofdesired temperatures and corresponding duty cycles. The processor mayalso be adapted to determine the microwave power or duty cycle inaccordance with the type of sample contained in the sample holder 210and/or the type of the sample tube.

It should be understood that any adequate conveyor system compatiblewith microwaves may be used. For example, the conveyor 206 may be a beltconveyor, a chain conveyor, a lineshaft roller conveyor, or the like.

In one embodiment, the sample holder 210 is provided with rollingelements rotatably secured therebelow. The conveyor 206 may comprise aplanar surface extending through the heating chamber 202, on which thesample holder 210 may roll, and a driving device adapted to roll thesample holder 210 on the planar surface. Any adequate driving mechanismmay be used.

It should be understood that any adequate sample holder 210 adapted tomicrowave heating may be used. For example, the sample holder may bemade from glass or Teflon. The sample holder may be adapted to receive asingle sample or a plurality of samples. For example, the sample holder10 or 120 may be used.

The heating chamber 202 may have any adequate shape and size forreceiving the sample holder 210 and can be made from any adequate typeof microwave-resistant material so that generated microwaves do not exitthe heating chamber 202.

In one embodiment, the conveyor 206 and the control unit 208 are adaptedto stepwise transport the sample holder 210. In this case, the sampleholder 210 occupies a series of predetermined positions during acorresponding predetermined period of time. In another embodiment, theconveyor 206 and the control unit 208 are adapted to continuously movethe sample holder 210 within the oven 200.

While the present description refers to a single heating chamber 202, itshould be understood that the oven 200 may comprise more than oneheating chamber each crossed by the conveyor 206 and each provided withmovable doors and a microwave generator. The heating chambers may bephysically secured together so that the sample holder 210 enters asecond heating chamber while exiting a first heating chamber.Alternatively, the heating chambers may be physically spaced apart.

FIG. 24 illustrates one embodiment of an automated microwave 230comprising a heating chamber 232 having a single opening 234 which isused for both entering and exiting the sample holder 210 and closed by asingle door. In this embodiment, the conveyor 238 may be U-shaped.

FIG. 25 illustrates one embodiment of a microwave oven 300 provided withthe same elements as the oven 200 and further comprising a coolingchamber 302. The cooling chamber 302 is adapted to receive the sampleholder 210 and the conveyor 206 extends through the cooling chamber 202.The cooling chamber 302 is positioned adjacent to the heating chamber302 so that the sample holder 210 may be brought into the coolingchamber 302 after leaving the heating chamber 202. The cooling chamber302 is provided with a cooling unit 304 adapted to cool the samplecontained into the sample holder 210. Any adequate cooling unit may beused. For example, the cooling unit may be a refrigerating unit. Inanother example, the cooling unit may comprise at least one fanpositioned to blow air on the sample holder 210 or draw air outside ofthe cooling chamber 302 in order to remove heat from the sample holder210 and cool the sample.

FIG. 26 illustrates one embodiment of a cooling chamber 320 providedwith three fans in order to cool the sample holder 210. An air outlet322 positioned near the top of the cooling chamber 320 and connected tothe outside of the oven 300 allows heated air to exit the coolingchamber 320. Three fans 324 are located near the bottom of the coolingchamber 320 and adapted to draw air contained in the cooling chamber 320outside thereof. When the fans 324 are operated, air contained in thecooling chamber 320 is expulsed outside and fresh air is drawn from theoutside into the cooling chamber 320, thereby creating an air currentwhich cools down the sample holder.

In one embodiment, the user enters cooling parameters such a coolingduration, a cooling unit power, a desired end cooling processtemperature, and/or the like in the control unit 208 which controls thecooling process in accordance with the cooling parameters.

In one embodiment, the oven 300 is free from any cooling chamber 202 andthe cooling device 304 such as a fan is located at the exit of theheating chamber 202.

FIG. 27 illustrates one embodiment of a microwave oven 350 comprisingall of the elements of the oven 300 and further comprising a ventingchamber 352 provided with an unsealing unit 354. When the sample holder210 is provided with a lid or cap for hermetically enclosing the sampleinto the sample holder 210, the unsealing unit 354 is adapted to unsealthe sample holder 210 so that pressurized gas contained in the sampleholder 210 may exit the sample holder 210. The control unit 208 isfurther adapted to control the unsealing unit 354. It should beunderstood that any adequate cap for hermetically sealing the sampleholder 210 and any adequate unsealing device adapted to unseal thesample holder 210 may be used.

In one embodiment, the sample holder 210 is provided with a thread sothat a lid may be screwed therein. The lid is screwed in the sampleholder 210 to hermetically close the sample holder 210 so that no gasmay exit the sample holder 210 during the heating process. In this case,the unsealing unit may comprise an automated arm provided with anyadequate mechanisms for unscrewing the lid such as pincers, a suctioncup, or the like.

In another embodiment, the sample holder may be the sample holder system10 and the unsealing device comprises a moving arm adapted to push onthe front portion of the clamping bar 51 in order to at least partiallydislodge the slot members 53 from the slots 25, as illustrated in FIG.28. The venting chamber 352 is provided with a movable arm 356 of whichthe displacement is controlled by a motor 358. By actuating the motor358, the movable arm 356 is moved towards the clamping bar 51 of thesample holder system 10 as illustrated in FIG. 28 (arrow E). The movablearm 356 then engages and pushes the clamping bar 51, thereby dislodgingthe slot members 53 from the slots 25 and unsealing the tubes 13.

In a further embodiment, the unsealing device may comprise a movable armprovided with pincers for pulling the rear end of the clamping bar 51.

In a further embodiment, the sample holder may comprise a clamping barhaving a safety mechanism such as the clamping bar 72 illustrated inFIG. 8. The unsealing device may comprise at least one moving armadapted to downwardly push on the locking member 84 to disengage thelocking member 84 from the stud 22 and horizontally push on the clampingbar 72 to dislodge the slot members from the stud slots. In oneembodiment, the moving arm is beveled in order to concurrently engagethe locking member 84 and the clamping bar 72 and exert a downward forceof the locking member 84 and a substantially horizontal force on theclamping bar 72.

In one embodiment, the venting process requires a precise positioning ofthe sample holder 210 with respect to the unsealing device 354. In thiscase, position sensors such as mechanical position sensors or opticalposition sensors may be used by the control unit 208 to determinewhether the position of the sample holder 210 within the venting chamber352 is adequate. If the control unit 208 determines that the position ofthe sample holder 210 is inadequate, a sample holder positioning devicecontrolled by the control unit 208 is used for moving the sample holderto an adequate position within the venting chamber 352. It should beunderstood that any adequate mechanical positioning device adapted tomove the sample holder to a desired position within the venting chamber352 may be used.

In another embodiment, no precise positioning of the sample holder 210with respect to the unsealing device 354 is required.

In one embodiment, the venting chamber 352 is fluidly connected to acooling chamber provided with at least one fan adapted to draw air outof the cooling chamber. In this case, gases leaking out of the sampleholder during the venting process are drawn out of the venting andcooling chambers by the fan.

In one embodiment, the heating chamber 202 and/or the cooling chamber302 and/or the venting chamber 352 is(are) provided with a temperaturesensor for measuring the temperature of the sample holder 210 and/or thesample contained in the sample holder 210. In this case, the controlunit 208 is adapted to control the microwave generator 204, the coolingunit 304, and/or the unsealing unit 354 in accordance with thetemperature of the sample holder 210 and/or the sample in the respectivechamber 202, 302, 352. For example, if a temperature sensor is presentin the heating chamber 202, or is positioned in such a way or such alocation to read a sample temperature in tube 132, the control unit 208can adjust the power and/or the duty cycle and/or the heating time ofthe generated microwaves in accordance with the sensed temperature toheat the sample up to a desired temperature. In another example in whichthe cooling chamber 302 is provided with a temperature sensor, thesample holder 210 may only exit the cooling chamber 302 when thetemperature of the sample and/or the sample holder 210 has decreasedbelow a predetermined temperature. The control unit 208 may also controlthe cooling unit 304 in accordance with the sensed temperature. In afurther example in which the venting chamber 352 is provided with atemperature sensor, the unsealing unit 354 is activated by the controlunit 208 only when the temperature of the sample holder 210 and/or thesample within the venting chamber 352 has decreased below apredetermined venting temperature.

In one embodiment, several sample holders 210 are positioned on theconveyor and are automatically brought to the heating chamber 202, thecooling chamber (if any), and the venting chamber (if any) by theconveyor 206. The control unit 208 may apply same parameters forheating, cooling, and/or venting all of the sample holders 210.Alternatively, the control unit 208 is adapted to apply differentparameters for each sample holder 210. For example, a first set ofparameters may be applied to the first sample holder, a second set ofparameters may be applied to the second sample holder, etc.

In one embodiment, each sample holder 210 is provided with anidentification (ID) device and the oven 200, 300, 350 is provided withan ID reader adapted to read the ID device. For example, the sampleholder 210 can be provided with a bar code and the oven 200, 300, 350can comprise a bar code reader. The user enters the bar code ID for eachsample holder 210 and the corresponding heating and/or cooling and/orventing parameters into the control unit 208 before starting the heatingprocess. When a sample holder 210 enters the heating chamber 202 orbefore entering in the heating chamber 202, the bar code reader readsthe ID of the sample holder 210 which is transmitted to the control unit208. The control unit 208 retrieves the heating parameters correspondingto the ID and controls the microwave generator 204 in accordance withthe heating parameters. The control unit 208 also retrieves the coolingand/or venting parameters from the memory and controls the coolingand/or venting processes in accordance with the retrieved cooling and/orventing parameters. In one embodiment, the bar code may comprise barsinked on the sample holder. In another embodiment, the bar code maycomprise slots made into the sample holder. In a further embodiment, atleast one magnet is used for identifying each sample holder 210 and theID reader is a magnetic reader. Alternatively, magnets are used torepresent binary numbers, and more than one magnet is used.

In another embodiment, the control unit 208 is provided with a clockwhich is used for identifying the sample holders 210. The control unitcan identify the different sample holders 210 using the heating timesand the time required for transporting the sample holders 210 from oneposition to another in the oven 200, 300, 350.

In one embodiment, the microwave oven 200, 300, 350 is sized and shapedto be portable. For example, in one embodiment, the entire system,including the heating chamber, the cooling chamber, and the ventingchamber as illustrated in FIG. 30, is 26 inches in height×26 inches inwidth×23.5 inches in depth. The heating chamber is 21 inches in width×13inches in height×4.5 inches in depth. The cooling and venting areas areeach 20 inches in width×19 inches in height×13.5 inches in depth. In oneembodiment, the rack is 14.7 inches in length×4 inches in width and canhave varying heights, such as 10 inches, 12.5 inches, etc. Thesedimensions are exemplary only and should not be construed as limiting.

FIG. 29 illustrates one embodiment of a microwave oven 450 comprisingall of the elements of the oven 400 but having a closed-loop conveyor360. The oven 450 may be used for heating a plurality of sample holderswithout any surveillance from a technician, over night for example. Asame sample holder may pass through the heating chamber 202, the coolingchamber 302 (if any), and the venting chamber 352 (if any) several timesto be heated, cooled, and/or vented several times.

In one embodiment, each sample holder 210 is provided with an ID and theoven 450 is provided with at least one ID reader. The user enters theheating and/or cooling and/or venting parameters for each ID into thecontrol unit 208 of the oven 450. When a sample holder enters theheating chamber 202 and/or the cooling chamber 302 and/or the ventingchamber 352, the control unit 208 identifies the sample holder 210 usingthe ID and applies the corresponding parameters retrieved from thememory. In one embodiment, the control unit 208 is adapted to count thenumber of sample holders 210 and stop the conveyor 360 when the lastsample holder 210 has completed the heating/cooling/venting cycle. Inanother embodiment, the control unit 208 is adapted to store the ID ofthe first sample holder entering the heating chamber 202 in order toidentify it as being the number one sample holder and to stop theconveyor when the number one sample holder is about to enter the heatingchamber for a second time. Alternatively, the control unit 208 isadapted to determine when the last rack of a series of pre-programmedracks exits the heating chamber 202 or the cooling chamber 302 or theventing chamber 352.

While in the present description, the heating chamber 202 of the ovens200, 300, 400, and 450 is provided with an entrance and an exit doorsfor preventing the microwaves from propagating outside of the heatingchamber 202, it should be understood that the heating chamber maycomprise a single door from allowing the entrance and exit of the sampleholder 210. In this case, the conveyor may be shaped to form a U-turninside the heating chamber 202.

While FIGS. 25, 27, and 29 illustrate a microwave oven in which theheating chamber 202, the cooling chamber 302, and/or the venting chamber352 are physically spaced apart, it should be understood that thechambers 202, 302, and 352 may be physically regrouped to form a tunnel.The microwave generator 204, the cooling unit 304, and the unsealingunit 354 are positioned along the tunnel at different positions. Atleast two microwave-barrier doors are positioned on each side of theheating chamber 202 to define a heating station within the tunnel.

FIG. 30 illustrates an automated digestion system 400 comprising amicrowave oven 402, a cooling station 404, a venting station 406, acontrol unit 408, and a conveyor (not shown). The automated digestionsystem 400 is adapted to receive fourteen sample holders 410 such assample holder systems 10 or 120, and successively heat, cool, and ventthem. As each sample holder 410 comprises twelve sample tubes, up to onehundred sixty eight samples may be digested in an automated fashion bythe automated digestion system 400, thereby provided an automateddigestion system having an improved throughput.

In one embodiment, the microwave oven 402 is removable from theautomated digestion system 400 and may be used in a non-automatedfashion. In this case, the user of the oven 402 manually inserts andremoves the sample holder 410.

In one embodiment, the control unit 408 applies the same heating and/orcooling and/or venting parameters to all of the sample holders 410. Inanother embodiment, the user may enter different operating parametersfor each sample holder 410.

FIG. 31 illustrates one embodiment of a conveyor 403 which may be partof the automated digestion system 400. The conveyor 403 comprises aplanar plate 412 on which sample holders 430-456 are deposited. Lowfriction feet or balls are rotatably secured below each sample holder430-454 so that the sample holder 430-456 may roll or slide on theplanar plate 412. The planar plate 412 is sized to receive fifteensample holders. However, only fourteen sample 430-456 holders are placedon the planar plate 412 so that an available position 458 is free fromany sample holder. The planar plate 412 is provided with fourrectangular openings under which a corresponding conveyor belt 420-426is positioned.

FIG. 32 illustrates one embodiment of the conveyor belt 422 whichcomprises a closed loop belt 470, two driving wheels 472 and 474, andtwo rack engaging members 476 and 478. The wheels 472 and 474 are drivenby at least one motor controlled by the control unit of the automateddigestion system. When the wheels 472 and 474 are anti-clockwiserotated, the rack engaging member 478 is moved towards the sample holder442, abuts against the rear portion of the sample holder 442, and exertsa force on the sample holder 442 which rolls to the next position.

Referring back to FIG. 31, the sample holder 430 is located in theheating chamber 402 while the sample holders 432 and 434 are in thecooling station and the venting station, respectively. Once the heatingof the sample holder 430 is completed, the conveyor belt 424 isactivated to move the sample holders 448-456 towards the availableposition 458. The position on top of the conveyor belt 424 becomes theavailable position as illustrated in FIG. 33. The conveyor belt 422 isthen activated to move the sample holders 442-446 towards the conveyorbelt 424. Once the sample holder 446 has reached the position on top ofthe conveyor belt 424, the position on top of the conveyor belt 422becomes the available position, as illustrated in FIG. 34. The conveyorbelt 420 is then activated to move the sample holders 432-440 towardsthe conveyor belt 422. Once the sample holder 440 reaches the positionon top of the conveyor belt 422, the position on top of the conveyorbelt 420 is available and the sample holder 432 is in the ventingstation of the automated digestion system, as illustrated in FIG. 35.Then the sample holder 430 is moved from the heating chamber 402 to thecooling station 404 while the sample holder 456 enters the heatingchamber 402. It should be understood that any mechanical positioningdevice may be used for moving a sample holder inside the heating chamber402 and moving a sample holder from the heating chamber to the coolingstation on top of the conveyor belt 420, and likewise from the coolingstation to the venting station

FIG. 37 illustrates one embodiment of a microwave oven 500 adapted toindependently heat six samples. The oven 500 comprises a chamber 502adapted to receive sample holders and provided with a microwave barrierdoor 504 for opening and closing the oven 500. The oven 500 alsocomprises six microwave applicators 506 each for individually applyingmicrowaves to a different sample holder. Each microwave applicator 506comprises a microwave generator 508 such as a magnetron for example, aflexible microwave waveguide 510 such as coaxial cable, and an ovencavity portion 512. The oven 500 further comprises a control unit 514adapted to control the microwave applicators 506. In this embodiment,the oven cavity portion 512 is movable with respect to the microwavegenerator 508 between an extended position and a retracted position(illustrated in FIG. 37) and the length of the flexible microwavewaveguide 510 is chosen to allow the displacement of the oven cavityportion 512 between the two positions.

FIG. 38 illustrates one embodiment of a sample holder 520 adapted to theoven 500. The sample holder 520 comprises a rack 522 adapted to receivesix sample tubes 524. The sample holder 520 also comprises six rackcavity portions 526. Each rack cavity portion 526 is adapted to form amicrowave cavity when physically connected to a respective oven cavityportion 512. The rack cavity portions 526 are positioned on the rack 522in accordance with the position of the oven cavity portions 512 when inthe extended position. It should be understood that the sample tubes 524may be removably secured to the rack 522.

FIG. 39 illustrates the sample holder 520 received in the microwave oven500. The sample holder 520 is positioned within the oven 500 so thateach rack cavity portion 526 faces a corresponding oven cavity portion512.

In one embodiment, a mechanical positioning device is used to preciselyposition the sample holder 520 within the oven 500. Positioning sensorssuch as optical or mechanical sensors may be used to determine theposition of the sample holder 520. It should be understood that themechanical positioning device may be controlled by the control unit 514of the oven 500.

In another embodiment, abutting elements are located in the oven 500 toprecisely position the sample holder 520 with respect to the oven cavityportions 512.

In a further embodiment, the sample holder 520 is positioned in the oven500 by a user.

Once the sample holder 520 has been precisely positioned in the oven500, the oven cavity portions 512 are moved from the retracted position(FIGS. 37 and 39) to the extended position, as illustrated in FIG. 40.In the extended position, each oven cavity portion 512 engages acorresponding rack cavity portion 526. As the oven cavity portion 512and the rack cavity portion 526 are complementary portions of a minimicrowave cavity 528, the mini microwave cavity 528 is formed when theoven cavity portion 512 engages the rack cavity portion 526. It shouldbe understood that the oven cavity portion 512 and the rack cavityportion 526 are made from microwave reflecting material such as metal,for example aluminum, and designed so that the mini cavity 528 issubstantially hermetical to microwaves, i.e. so that substantially nomicrowaves exit the cavity at the junction of the oven cavity portion512 and the rack cavity portion 526.

While the present description refers to a rack 520 having six rackcavity portions 526 and an oven 500 having six oven cavity portions 512,it should be understood that the number of cavity portions is exemplaryonly as along as the rack 520 and the oven 500 each comprise at leasttwo respective cavity portions.

While FIGS. 37 to 40 illustrate an oven 500 comprising two rows ofphysically spaced oven cavity portions 512 and a rack 520 comprising tworows of physically spaced rack cavity portions 526, it should beunderstood that other embodiments are possible. For example, FIG. 41illustrates one embodiment of a microwave oven 530 comprising two ovencavity elements 532 each having three recesses 534 each forming an ovencavity portion. The oven 530 is adapted to receive a sample holder 536comprising a rack 538 on which two rack cavity elements 540 are secured.Each rack cavity element 540 comprises three recesses 542 each forming arack cavity portion.

While FIG. 37 illustrates an oven 500 comprising movable oven cavityportions 512, it should be understood that other embodiments arepossible. For example, FIG. 42 illustrates one embodiment of a microwaveoven 550 comprising six movable microwave applicators 552. Eachmicrowave applicator 552 comprises a microwave generator 554 and an ovencavity portion 558 connected together by a microwave waveguide 556. Themicrowave waveguide 556 may be flexible. Alternatively, the microwavewaveguide 556 may be rigid. The microwave applicators 552 are secured totwo displacement plates 560 to form two rows of microwave applicators552. By moving one displacement plate 560, three microwave applicators552 are moved. Alternatively, each microwave applicator 552 may beindependently movable.

While FIG. 40 illustrates a mini microwave cavity 528 designed to matchthe shape of the sample tube 524, it should be the mini cavity may haveany adequate shape and size. FIG. 43 illustrates one embodiment of asquare mini microwave cavity 570 formed when an oven cavity portion 572engages a rack cavity portion 574. The internal perimeter of the squaremini microwave cavity 570 is superior to the external perimeter of thecylindrical sample tube 524 so that the sample tube 524 does not engagethe walls of the cavity 570.

FIG. 44 illustrates one embodiment of a mini microwave cavity 580 formedby engaging an oven cavity portion 582 with a rack cavity portion 584.The oven cavity portion comprises a U-Shaped microwave reflecting plate586 having an internal groove and a protective element 588 positioned inthe groove of the plate 586. An antenna 590 having a shape matching thatof the groove is inserted between the plate 586 and the protectiveelement 588. The antenna may be curved, vertical, or other. The antenna590 is connected to a power generator via a microwave waveguide 592 andis used to emit microwaves in the cavity 580. The rack cavity portion584 comprises a U-shaped microwave reflecting plate 594 having a groovein which a protective element 596 may be inserted.

The protective elements 588 and 596 are made from a material transparentto microwaves such as Teflon for example, while the U-shaped plates 586and 594 are made from a material capable of reflecting microwaves suchas metal (aluminum, etc).

It should be understood that the mini microwave cavity may have anyadequate height with respect to that of the sample tube to be receivedtherein. For example, the height of the oven and rack cavity portionsmay be substantially equal to that of the sample tube. Alternatively,the height of the oven and rack cavity portion may be less than that ofthe sample tube.

FIG. 45 illustrates one embodiment of an automated digestion systemprovided with a control unit (not shown) and a closed loop conveyor fordirecting a plurality of sample holders 604 in a heating chamber 605, acooling station 606, and a venting station 608. Each sample holder 604comprises at least one rack cavity portion 610 adapted to receive ahermetically closed or open sample tube 612. The heating chamber 605 isprovided with at least one movable oven cavity portion 614 connected toa microwave generator and adapted to form a mini microwave cavity whenconnected to a corresponding rack cavity portion 610. In someembodiments, two or more rack cavity portions 610 are provided in theheating chamber 605.

When a sample holder 604 enters the heating chamber 605, a positioningdevice (not shown) precisely positions the sample holder 604 withrespect to the position of the oven cavity portions 614. Then, the ovencavity portions 614 are moved to their extended position in order toengage their respective rack cavity portion 610, thereby forming a minimicrowave cavity.

The sample contained in each sample tube 612 may be independently heatedby applying sample specific parameters. The independent mini microwavecavities allow each individual sample to be heated to a sample specifictemperature, for a sample specific amount of time. Therefore, eachsample of a sample holder 604 containing a given number of samples maybe different, and the sample specific parameters can be applied to eachsample accordingly. Various heating programs may be created using acombination of heating and non-heating times and a plurality of heatingtemperatures. The sample holder 604 is maintained in the heating chamber605 until the last sample has completed its heating program.

The sample-specific heating parameters may comprise a desiredtemperature, and/or a microwave power, and/or a duty cycle, and/or aheating time, and/or sample parameters such as an identification of thesample or the quantity of sample contained in the sample tube, and/ortube parameters such as the volume of the tube or the material of thetube, and/or the like. The automated digestion system 600 is adapted toidentify a particular sample tube 612 and independently heat each sampletube 612 in accordance with the sample specific parameters. In oneembodiment, the automated digestion system 600 is provided with a barcode reader and the sample parameters are retrieved by the control unitby reading the bar code of the sample container.

In one embodiment, the sample holder 604 is provided with an ID, such asa bar code or a RF ID for example, for each sample tube 612 and theautomated digestion system 600 is provided with an ID reader adapted toread the sample tube ID. Alternatively, the sample ID may be located onthe sample tube 612.

In another embodiment, the rack is provided with an internal clock andthe automated digestion system 600 is provided with a reader capable ofidentifying the sample holders 604 using the internal clock. One seriesof magnets are used to activate a sensor (the reader), and anotherseries of magnets are used as the clock. The clock corresponds to an IDfor the sample holder 604.

Once the heating process is completed, the oven cavity portions aremoved to their retracted position and the sample holder 604 is moved tothe cooling station 606 to be cooled. Once cooled, the sample holder 604is brought to the venting station 608 where an unsealing system unsealsthe sample tubes, thereby providing an auto-venting of the sample tubes.In one embodiment, moving the sample holder 604 from the cooling station606 to the venting station 608 occurs when the samples in the sampletubes 612 at the cooling station 606 have reached a pre-determinedtemperature.

FIG. 46 illustrates one embodiment of mini microwave cavities 650 eachcomprising a temperature sensor 652 for sensing the temperature of asample contained in a vessel or sample tube 654. In this embodiment, thetemperature sensors sit below each vessel underneath a floor of theheating chamber. A series of apertures are provided in the floor of theheating chamber to allow the temperature sensors to access the vessels.Individual temperature control of each sample in each vessel isprovided.

Each mini cavity 650 is formed by a movable oven cavity portion 656 anda rack cavity portion 658. An antenna 660 is connected to a microwavesource 662 by a microwave waveguide 664. For each mini cavity 650, aproportional-integral-derivative (PID) controller 666 receives thesensed temperature from a temperature sensor 652. In order to reach adesired sample temperature, the PID controller 666 adjusts the amount ofmicrowave energy delivered by the microwave source 662 to the antenna660 by controlling an adjustable high voltage current source 668powering the microwave source 662. Although FIG. 46 illustrates aconfiguration comprising one microwave source per mini cavity, anotherembodiment may comprise one microwave source and a splitter for multiplecavities.

FIG. 47 illustrates one embodiment of a sample holder 670 comprising therack cavity portions 658. The sample holder 670 comprises a rack formedby a base plate 672 and a stud 674, and a rack cover 676. The rack covercomprises a cap-receiving plate 678 to which compression caps 680 areremovably secured. The vessels 654 are received in the rack and sealedby a sealing cap 682. Then the rack cover 676 is secured on top of therack so that a compression cap 680 abuts against a corresponding sealingcap 682 for hermetically closing the vessels 654.

In an alternative embodiment, open vessels are used that do not requirethe rack cover plate 676. In this case, cap 682 may or may not be set ontop of the vessel 654.

While the sample holder 670 is provided with a rack cover 676 providedwith a pressure-relief valve system, it should be understood that thevessels 654 may be closed by the sealing caps 682. Alternatively, thevessels 654 may be left open during the heating process.

In one embodiment, each vessel 654 contains a sample 690 and a liquidsolution 692 and is positioned into its respective mini cavity 650 sothat the sample 690 and the solution 692 present an RF load matchingthat of the antenna 660. This maximizes energy transfer to the solution692 and minimizes energy reflection towards the microwave source 662.

FIG. 48 illustrates one embodiment of a mini cavity assembly 700 inwhich the rack cavity portions are made of a single piece. The rack 702comprises a cavity element 704 in which grooves 706 are made on oppositesides thereof. Each groove 706 corresponds to a rack cavity portion anda sample tube 708 is inserted into the grooves. Oven cavity portions 710are regrouped into two rows and each row of oven cavity portions 710 issecured to a translation plate 712. The translation plates 712 areactivated by a motor (not shown) to engage the oven cavity portions 710with the rack cavity element 704 to form the mini cavities.

FIG. 49 illustrates one embodiment of a rack 750 provided with rackcavity portions and a microwave cross-talk preventing device. The rack750 comprises a base plate 752 to which a cavity plate 754 and aU-shaped plate 756 are secured. Recesses 758 are made in the cavityplate 754 to form six rack cavity portions on each side of the cavityplate 754. Twelve openings 760 each aligned with a recess 758 andadapted to receive a sample tube 762 are made on top of the cavity plate754. The U-shaped plate 756 is provided with twelve tube receivingopenings 764 each aligned with a respective opening 760. The rack 750further comprises twelve microwave reflecting cylinders 766 each securedon top of the cavity plate 754 and aligned with a respective opening 760so that a sample tube 762 may be received in the openings 760 and 764and the hollow cylinder 766. The reflecting cylinders 766 serve as amicrowave cavity extender to prevent cross talk and extend the microwaveenergy to samples that exceed the size (volume) of the microwave cavity.

The rack 750 is inserted into a heating chamber provided with ovencavity portions matching the rack cavity portions to form twelve minimicrowave cavities. The cylinders 766 acts as a microwave barrierreducing or substantially preventing the propagation of microwaves fromone mini cavity to another. It should be understood that the cylinders766 are made from a microwave reflecting material such as metal oraluminum for example.

In one embodiment, an automated digestion system such as the system 400is provided with a heating chamber comprising at least oven cavityportions and adapted to receive a rack comprising rack cavity portions.For example, the rack 750 may be used for heating samples in such anautomated digestion system.

In one embodiment, the base plate 752 of the rack 750 is provided with atoothed groove 770 adapted to engage a gear having mesh teeth. The gearmay be located in the heating chamber for precisely positioning the rack750 in the heating chamber so that each rack cavity portion faces itsrespective oven cavity portion. The gear may also be used to bring therack in the heating chamber and/or the cooling chamber.

In one embodiment, the base plate 752 is provided with at least fourballs or low friction feet rotatably secured thereto for allowing therack 750 to roll or slide on a substantially planar surface. In oneembodiment, the front portion of the rack 750 must firstly enter in theheating chamber. In this case, only one side of the groove 770 isprovided with teeth. This allows the gear not to engage with the grooveif the rear portion of the rack is firstly presented to the gear.

In one embodiment, the base plate 752 is provided with twelve base plateopenings each located beneath a corresponding sample tube 762 and theheating chamber is provided with twelve temperature sensors such as IRsensors. When the rack 750 enters the heating chamber and the minicavities are formed, each temperature sensor is positioned below arespective base plate opening for measuring the temperature of arespective sample contained in the corresponding sample tube 762.

FIG. 50 illustrates one embodiment of a reflected power measuring device800 for measuring the power reflected by a microwave cavity 802. Themicrowave cavity 802 is connected to a microwave generator 804 by acoaxial cable 806. The measuring device 800 comprises a directionalcoupler having a first RF waveguide 808 coupled to a second RF waveguide810. The first and second RF waveguides 808 and 810 are spaced apart bya distance corresponding to a quarter of the wavelength of the RF signalpropagating between the microwave generator 804 and the microwave cavity802. The distance could also be ¾ of the wavelength, 5/4 of thewavelength, etc. The coaxial cable 806 comprises a central core 814 anda shield 816 separated by a dielectric 818. Two holes 820 and 822 aremade in the shield 816 of the coaxial cable 806. The two holes 820 and822 are spaced apart by a distance corresponding to a quarter of thewavelength of the RF signal propagating between the microwave generator804 and the microwave cavity 802. The first end 824 of the firstwaveguide 808 is inserted into the first hole 820 while the first end826 of the second waveguide 810 is inserted into the second hole 822.

When an RF signal propagates from the microwave generator 804 to themicrowave cavity 802, a part of the signal propagating in the core 814of the coaxial cable 806 leaks via the first and second holes 820 and822 and is coupled to the first end 824 of the first waveguide 808 andto the first end 826 of the second waveguide 810. Because the length ofa third waveguide 812 is equal to the quarter of the wavelength of theRF signal, no signal propagates at the output 828 of the firstwaveguide. As illustrated in FIG. 51, at the tee junction in port 4, thesignal coming from hole 820 is split in two parts, one going to port 3and another going up to the output 828. At the tee junction in port 3,the signal coming from hole 822 is split in two parts, one going to port4 and another going up to the output 830. The signal coupled at port 3is going in the opposite direction and will be subtracted at port 4.Because the separation between the ports 3 and 4 is equal to a quarterwavelength, the signal coming from port 4 and going towards the output828 is cancelled. As a result only one signal exits the directionalcoupler 800 by the output 830. The signal collected at the output 830may be used for determining the power of the RF signal propagating fromthe microwave generator towards the microwave cavity 802.

FIG. 51 illustrates the propagation of an RF signal reflected by thecavity 802 and propagating from the cavity 802 towards the microwavegenerator 804. Following the same reasoning as for a signal propagatingfrom the generator 804 towards the cavity 802, no signal is propagatedtowards the output 830 while the signal exiting the coupler 800 at theoutput 828 may be used for determining the power of the signal reflectedby the cavity 802.

In one embodiment, the waveguides 808, 810, and 812 are microstriplines. In another embodiment, the waveguides 808, 810, and 812 arestriplines.

In one embodiment, because the coaxial cable 806 is part of thedirectional coupler, the cable 806 is not sliced in multiple sections tobuild a coupler and a high decoupling factor is obtained, therebyrendering the coupler 800 adequate for high power applications.

In one embodiment in which the RF signal propagation speed in thewaveguides 808, 810, and 812 and in the coaxial line 806 are different,the coupler 800 comprises a dielectric substrate on which the waveguides808, 810, and 812 are deposited and the dielectric constant of thesubstrate is chosen to render the RF signal propagation speed in thewaveguides 808, 810, and 812 substantially equal to that in the coaxialcable 806. In the case where the propagation speed of a signal in acoaxial line is larger than in microstrip or stripline, the separationof holes 820 and 822 is equal to ¼ of wavelength in the coaxial cableand the length of line 812 is equal to ¾ wavelength. In this case, thecoupled signal when the propagation is coming from generator 804 tocavity 802 will be at 828 and canceled at 830, and vice versa forreflecting signals.

In one embodiment, the hole is sized so that the coupling factor betweenthe coaxial cable 806 and the coupler 800 is about −55 dB or less. Thisconfiguration is suitable for high power applications. In otherembodiments, the coupling factor could be other than −55 dB for lowpower applications.

FIG. 52 illustrates one embodiment of a coupler 850 comprising adetecting diode 852 used for measuring the power of a signal propagatingin the first waveguide 854 and therefore determining the microwave powerreflected by the cavity. The coupler 850 further comprises a seconddetecting diode 856 used for measuring the power of a signal propagatingin the second waveguide 858 and therefore determining the microwavepower generated by the microwave generator.

In one embodiment, the isolation between the ports is substantiallyequal to −10 dB.

In one embodiment, a matching on output ports is achieved in order tomaintain a good isolation between the cavity 802 and port 3, and themicrowave generator 804 and port 4.

FIG. 53 illustrates one embodiment of a coupler provided with a detectorfor measuring the reflected power and another detector for measuring theincident power. Each detector comprises a Schottky zero bias diode thattransforms the microwave signal into a DC voltage. In one embodiment,the detector is linear in the square law range means below −5 dBm. Inone embodiment in which the coupling factor is about −55 dB, thedetector is substantially linear for input powers as large as 50 dBmmeans 100 Watts, and can detect powers up to 60 dBm means 1000 Watts. Inone embodiment, an input resistor is used to match the circuit and theresult is about −15 dB which is lower than the directivity of coupler.

In one embodiment, the detected reflected power is used for determiningcavity problems such as a missing sample tube, the complete evaporationof the sample contained into the cavity, the absence of a sample into asample tube, the explosion of a sample tube, and the like. Upondetection of a problem, the generation of microwaves may be stopped andan alarm may be triggered.

In one embodiment, the detected incident power may be used for detectingmicrowave source problems.

While the present description refers to digestion of samples, it shouldbe understood that the methods, apparatuses, devices, and systemdescribed above may be used for extraction.

It should be noted that the embodiments described above are intended tobe exemplary only. Solely the scope of the appended claims islimitative.

We claim:
 1. A method for heating a sample material in a sample holder,the method comprising: receiving the sample holder in a heating chamberof a heating system, the sample holder having at least one samplerecipient with the sample material therein; dynamically forming anindividual mini microwave cavity around the at least one samplerecipient inside the heating chamber by mating a set of first partialmini cavities with a set of complementary second partial mini cavities,wherein the set of first partial mini cavities are in the heatingchamber and the set of complementary second partial mini cavities are onthe sample holder; and applying microwaves generated by at least onemicrowave generator directly to the sample in the at least one samplerecipient within the mini microwave cavity.
 2. The method of claim 1,further comprising mechanically positioning the sample holder in theheating chamber to align the set of first partial mini cavities with theset of complementary second partial mini cavities.
 3. The method ofclaim 1, wherein dynamically forming an individual mini microwave cavitycomprises forming a plurality of individual mini microwave cavitiesaround each one of a plurality of sample recipients in the sampleholder.
 4. The method of claim 3, wherein applying microwaves comprisesapplying microwaves generated using at least two separate microwavegenerators.
 5. The method of claim 4, wherein applying microwavescomprises applying microwaves according to an independent heatingschedule with sample specific parameters for each one of the at leasttwo separate microwave generators.
 6. The method of claim 5, wherein thesample specific parameters comprise at least one of a desiredtemperature, a microwave power, a duty cycle, a heating time, anidentification of the sample, a quantity of the sample, a volume of thesample recipient.
 7. The method of claim 3, wherein each mini microwavecavity has its own microwave generator.
 8. The method of claim 1,wherein receiving the sample holder comprises receiving the sampleholder on a conveyor that transports the sample holder into the heatingchamber.
 9. The method of claim 8, further comprising transporting thesample holder out of the heating chamber on the conveyor after a heatingprocess.